U.S. patent number 5,512,161 [Application Number 08/404,173] was granted by the patent office on 1996-04-30 for process for galvanically forming structured plate-shaped bodies.
This patent grant is currently assigned to Kernforschungszentrum Karlsruhe GmbH. Invention is credited to Heinz Dinglreiter, Helmut Kalb, Richard Rapp.
United States Patent |
5,512,161 |
Dinglreiter , et
al. |
April 30, 1996 |
Process for galvanically forming structured plate-shaped bodies
Abstract
In a process for galvanically forming structured plate-like
bodies, wherein a layer of a plastic material is structured at one
side and structure bodies with plane front surfaces are formed
thereon so as to rise from a contiguous electrically conductive
base, the front surfaces of the structure bodies are provided with
isolated spangles of electrically conductive material which are
electrically insulated from each other and sized and spaced such
that a line across a front surface intersects at least one of the
spangles and the structure base--used as a cathode--and the
structured bodies are then galvanically covered with a metal to
form the structured plate on the layer of plastic material.
Inventors: |
Dinglreiter; Heinz (Forst,
DE), Kalb; Helmut (Eggenstein-Leo., DE),
Rapp; Richard (Stutensee, DE) |
Assignee: |
Kernforschungszentrum Karlsruhe
GmbH (Karlsruhe, DE)
|
Family
ID: |
6468563 |
Appl.
No.: |
08/404,173 |
Filed: |
March 6, 1995 |
Foreign Application Priority Data
|
|
|
|
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Sep 23, 1992 [DE] |
|
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42 31 742.8 |
|
Current U.S.
Class: |
205/67;
205/70 |
Current CPC
Class: |
B29C
59/026 (20130101); B81B 1/00 (20130101); C25D
1/10 (20130101); B29C 2059/023 (20130101) |
Current International
Class: |
B29C
59/02 (20060101); B81B 1/00 (20060101); C25D
1/00 (20060101); C25D 1/10 (20060101); C25D
001/10 () |
Field of
Search: |
;205/67,70,118,75,76,122,68,69 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
0273552 |
|
Jul 1988 |
|
EP |
|
0331208 |
|
Sep 1989 |
|
EP |
|
0476867 |
|
Mar 1992 |
|
EP |
|
1621034 |
|
Feb 1967 |
|
DE |
|
3442781 |
|
Jun 1989 |
|
DE |
|
4010669 |
|
Apr 1991 |
|
DE |
|
Other References
Abstract of JP Kokei No. 53-106643. .
Patent Abstract of Japan, C-861, Aug. 23 vol. 15, No. 332..
|
Primary Examiner: Niebling; John
Assistant Examiner: Mee; Brendan
Attorney, Agent or Firm: Bach; Klaus J.
Claims
What is claimed is:
1. A process for galvanically forming a structured plate,
comprising the steps of:
a) providing a layer of a plastic material,
b) structuring said plastic material layer at one side thereof such
that structure bodies with planar front surfaces are formed
thereon,
c) the structuring being done in such a way that the structure
bodies rise from a structure base which forms contiguous
electrically conductive surfaces and said front surfaces of said
structure bodies extend parallel to said structure base,
d) providing on said front surfaces isolated spangles of an
electrically conductive material which are electrically insulated
from each other by:
d.1) coating said plastic material surfaces to be structured with
an electrically conductive material,
d.2) impressing a structured metal stamp into the surface coated
with said electrically conductive material such that the coating of
electrically conductive material is divided into a part disposed at
the bottom of recesses formed into said plastic material layer by
said impressing step and a part remaining on the raised front
surface areas of said structure bodies and
d.3) cutting the raised front surface areas with the electrically
conductive material thereon down to the electrically conductive
material in said recesses which remains on the front surfaces of
said structure bodies and then forms said isolated electrically
conductive spangles sized and arranged at a distance from each
other such that a line across the front surfaces of a structure
body in any direction intersects at least one of said spangles
and
e) galvanically covering said structure base and said structure
bodies with a metal to form said structured plate on said layer of
plastic material.
2. A process according to claim 1, wherein said layer of plastic
material consists of a thermoplast.
3. A process for galvanically forming a structured plate,
comprising the steps of:
a) providing a layer of a plastic material,
b) structuring said plastic material layer at one side thereof such
that structure bodies with planar front surfaces are formed
thereon,
c) the structuring being done in such a way that said structure
bodies rise from a structure base which forms a contiguous
electrically conductive surface and the front surfaces of said
structure bodies extend parallel to the structure base,
d) providing on said front surfaces isolated spangles of an
electrically conductive material which are electrically insulated
from each other by:
d.1) applying a layer of electrically conductive material on said
front surfaces,
d.2) coating said electrically conductive material on said front
surfaces with a layer of a light sensitive photolacquer,
d.3) placing on said photolacquer layer a mask with light
transmissive areas and opaque areas where said spangles are to be
provided,
d.4) exposing said front surfaces with said mask disposed thereon
to light,
d.5) eliminating said photolayer coating under said light
transmissive areas and said layer of electrically conductive
material underneath, and
d.6) removing the non-irradiated photolacquer layer so as to expose
the electrically conductive areas underneath thereby providing said
spangles which are sized and arranged at a distance from each other
such that a line across the front surfaces of a structure body in
any direction intersects at least one of said spangles and
e) galvanically covering said structure base and said structure
bodies with a metal to form said structured plate on said layer of
plastic material.
4. A process for galvanically forming structured plate shaped
bodies, comprising the steps of:
a) providing a layer of a plastic material,
b) structuring said plastic material layer at one side thereof such
that structure bodies with planar front surfaces are formed
thereon,
c) the structuring being done in such a way that said structure
bodies rise from a structure base which forms a contiguous
electrically conductive surface and said structure bodies have
front surfaces which extend parallel to said structure base.
d) providing on said front surfaces isolated spangles of an
electrically conductive material which are electrically insulated
from each other by:
d.1) coating said front surfaces of said structure bodies with a
layer of a light sensitive photolacquer,
d.2) placing on said light sensitive photolayer a mask with light
transmissive areas where said spangles of electrically conductive
material are to be formed on the front surfaces underneath,
d.3) exposing said mask to light,
d.4) removing the light irradiated areas of said photolacquer layer
to form recesses where said spangles are to be formed,
d.4) covering said front surfaces with an electrically conductive
material and
d.5) machining said front surfaces to remove the light conductive
material from said front surfaces except for the conductive
material in said recesses thereby forming said isolated spangles of
conductive material on said front surfaces of said structure bodies
so that they are sized and arranged at a distance from each other
such that a line across the front surfaces of a structure body in
any direction intersects at least one of said spangles and
e) galvanically covering said structure base and said structure
bodies with a metal to form said structured plate on said layer of
plastic material.
Description
This is a continuation-in-part application of international
application PCT/EP93/02482 of Sep. 14, 1993 claiming the priority
of German application P 42 31 742.8 filed Sep. 23, 1992.
BACKGROUND OF THE INVENTION
The invention resides in a method of galvanically forming
structured plate-like bodies which are structured at one side such
that the structures project from a base representing a contiguous
electrically conductive surface to which the structure tops are
parallel wherein the base is galvanically covered by a metal.
In microstructuring techniques, it is often necessary to
galvanically form, by metal deposition, a structure from a plastic
plate provided with micro structured bodies by means of
microforming techniques or X-ray depth lithography. The
microstructured bodies on the plastic plate are formed in such a
way that the structure base, that is the surface from which the
microstructures rise, is electrically conductive. The easiest way
to provide such an electrically conductive surface is to attach the
plastic plate to a metal plate and to remove plastic material
around the microstructures to be formed down to the metal plate so
that the microstructures are disposed directly on the metal plate
and the exposed portions of the metal plate form the structure
base. Negative shapes of the microstructured bodies can then be
formed galvanically in a galvanic bath in which the metal plate is
used as a cathode. In this process, first the interstices between
the structured bodies are filled from the structure base on. Upon
continuation of the galvanic process, the micro structured bodies
are finally covered with metal as the nonconductive microstructured
body front surfaces are overgrown. At the end of the process, the
microstructured bodies are totally embedded in the metal. Such a
process is disclosed for example in U.S. Pat. No. 5,073,237. A
process for the galvanic forming of plate-like bodies provided with
microstructures is disclosed in this patent. The process described
therein serves to provide negative forms of microstructured
plate-like bodies which can serve as galvanic molds and whose
structure base is a contiguous surface covered with a layer of an
electrically conductive material, wherein the electrically
conductive material layer is used as a cathode in the subsequent
galvanic forming step.
The process utilizes a thermoplastic material layer on which a film
of an electrically conductive material is deposited. A
microstructured mold insert is impressed into the thermoplastic
material layer through the electrically conductive material and is
then again removed. With this process, a continuous electrically
conductive structure base is formed. During impression of the mold
insert into the film-covered thermoplastic material layer, the film
ruptures where it is engaged by the micro structures of the mold
insert. Upon removal of the mold insert, small, isolated spangles
of the film material, which are electrically insulated from one
another remain on the vertical wall portions and on the front faces
of the microstructures. On the structure base of the negative form
however, the film remains undisturbed. With regard to the spangles
remaining on the micro structure surfaces of the negative form, it
is pointed out that, because of their isolated arrangement, they
are electrically insulated from the structure base and therefore,
do not prevent exact galvanic forming from the negative mold.
The purpose of this method resides in the formation of a
contiguous, electrically conductive structure base which is fully
covered by the film of electrically conductive material. The
isolated spangles of the film occur as side effects and are
therefore--dependent on the thickness of the film and on the shape
of the micro structures--distributed on the microstructures in an
incidental and non-reproducible manner.
In accordance with the Abstract of J. P. Kokei No. 53-106 643, a
plastic substrate is, by means of a molding tool, so structured
that concave depressions and convex structure bodies are generated.
The plastic substrate is subsequently coated over its whole surface
with a thin layer of an electrically conductive material. Then,
only those parts of the electrically conductive material are
removed which are disposed on the front faces of the convex
structure bodies. Subsequently, the concave depressions are
galvanically filled with the electrically conductive material. The
electrically conductive material projecting beyond the from
surfaces of the convex structure bodies is then removed. Since the
galvanically deposited material and the convex structure bodies are
to have the same height, no problems are encountered by the
overgrowth of the galvanic deposits over the front faces.
DE 34 42 781.C2 discloses a method of producing an adjustment disc
for cameras wherein a regular relief structure is formed on the top
surface of a metal plate by mechanical treatment thereof. The
relief structure is then subjected to normal galvanic treatment
wherein an emulsion is added to the galvanizing bath which, with a
local and timely statistical distribution, inhibits the galvanic
deposition and forms the pattern obtained thereby, onto an optical
material. With the known method, a metal is galvanically deposited
on the whole mechanically structured metal plate, the structure
base as well as the structure bodies are electrically conductive.
The emulsion inhibits the galvanic deposition on small
statistically distributed spots.
The publication Patent Abstracts of Japan, C-861, Aug. 23, 1991,
Vol. 15, No. 332 [Abstract of JP 3-126,887(A)] describes a method
wherein metal powder such as nickel powder, is admixed to a liquid
resin. The resin with the metal powder is then filled into a
negative form and is cured. The surface of the cured resin is then
ground so that a smooth surface is generated on which the powder is
exposed. The mold is then placed in a galvanic cell wherein nickel
is deposited on the surface of the mold in order to provide a space
for the galvanic deposition. In this process, the form does not
need to be directly polished since, in this case, the resin is made
electrically conductive by the addition of a metal powder.
Relatively high concentrations of metal powder have to be used
which noticeably change the properties of the resin.
DE-OS16 21 034 discloses a method of making a mold for the
galvano-plastic manufacture of sieves, cuttable foils, filters,
grids, or similar articles wherein a light sensitive photo layer is
disposed on a polished, cleaned metal plate and is exposed to light
with the desired pattern. After being developed, the areas exposed
to light are covered and the non-exposed areas are dissolved and
the metal plate is then etched at the exposed areas to form
depressions. According to this known process, the metal plate with
the etched depressions from which the exposed photolayer has been
removed, is covered and the etched depressions are filled with a
hardenable electrically conductive plastic. After hardening, the
metal plate and the layer of electrically conductive plastic, not
the metal plate, is used for the galvanic molding procedure.
The plastic layer is electrically conductive at all structure
areas. The process is not concerned with the galvanic molding.
The present invention is concerned with the problem of evenly
growing galvanically deposited material over an electrically
non-conductive surface as it is present in the initially referred
to normal case on the front surface of structured plastic bodies.
The galvanic overgrowth over the front surface of the structure
bodies starts at an electrically conductive base, which, as
initially mentioned, is slowly built up and fills the depressions
or cavities until the microstructure bodies are overgrown and
embedded.
This galvanic procedure involves two different processes: the
vertical growth in which deposition of the material to be
galvanically deposited occurs by way of an electrically conductive
metal layer serving as a cathode or on the metal already deposited
on the metal layer, and the lateral growth which occurs when the
level of the front surface of the microstructures has been reached
whereby those front surfaces are finally fully covered with
metal.
The speed of the lateral growth under the usual galvanization
conditions (nickel sulfate electrolyte, current density
1A/dm.sup.2) is normally on the same order as the vertical growth,
that is, it is about 12 .mu./h. During the galvanic overgrowth of
stepped structured bodies, it is even possible that faults occur at
the level of the intermediate and the upper front surfaces when the
galvanic growth fronts meet.
Basically, it would seem helpful to apply to the front faces of the
structured bodies a continuous conductive layer which is isolated
from the structure base. In this manner, a lateral growth could be
achieved with increased speed with regard to the vertical growth.
In this case, a sudden contact of the adjacent front faces with the
metal grown between the micro-structured bodies would render the
whole front face areas cathodic. However, since the rate of metal
deposition between the structured bodies is uneven, the formation
of such sudden contacts may have the result that further vertical
growth in the areas where the galvanic growth has not yet reached
the front faces of the structured bodies is interrupted by the
galvanic lateral growth. The result will then be that some of the
particular structured bodies are not formed and are missing in the
galvanically deposited body. At these locations, the galvanically
formed product will have cavities. This effect will be greater for
larger aspect ratios (relation of height to the width of the
bodies) of structured bodies and for greater aspect ratio
differences in a particular micro-structure.
It is the object of the present invention to provide a method with
which the problems related to the cross-sectional growth of
galvanically deposited metal structures are prevented.
SUMMARY OF THE INVENTION
In a process for galvanically forming structured plate-like bodies,
wherein a layer of a plastic material is structured at one side and
structure bodies with plane front surfaces are formed thereon so as
to rise from a contiguous electrically conductive base, the front
surfaces of the structure bodies are provided with isolated
spangles of electrically conductive material which are electrically
insulated from each other and sized and spaced such that a line
across a front surface intersects at least one of the spangles and
the structure base--used as a cathode--and the structured bodies
are then galvanically covered with a metal to form the structured
plate on the layer of plastic material.
The invention is not limited to microstructures. It can also be
utilized for the manufacture of larger structures measured in
millimeters.
An essential feature of the method according to the invention is
that, on the structure body front surfaces, an array of small
isolated spangles is formed. The size of the particular spangles
depends on the size of the front surfaces of the structure bodies.
The largest diameter of the particular spangles should be such that
several spangles are disposed on each front face in each direction.
If the front face of a structured body has, for example a stepped
shape, the diameter of the spangles should be such that also over
the width of a step there is space for at least one isolated
spangle. All the front faces must be covered with the pattern of
spangles before the galvanizing process begins and in each
direction there should be at least one spangle.
In principle, such a pattern can be generated before or after the
structuring of the plate. In each case, the arrangement described
above can be produced before the galvanizing step. If one starts
out with a plastic plate covered with a layer of electrically
conductive material, the spangle pattern can be generated already
on this arrangement before structuring takes place. For the spangle
sizes, the dimensions of the front surfaces to be subsequently
generated have to be considered, of course. But the pattern of
spangles may also be provided on the front faces of the structure
bodies after they have been formed.
Such a pattern cannot be formed in accordance with the method given
in U.S. Pat. No. 5,073,237 discussed earlier, since, in this
publication, the spangles are formed in a non-reproducible manner
and have an accidental size distribution.
With the method according to the invention, the galvanic overgrowth
of the front faces occurs in such a way that the various spangles
which have already been electrically contacted by the vertical
growth provide for a step-like increasing galvanic deposition area
on the front faces of the structures. Since the spangles themselves
are electrically conductive, metal is deposited on the whole
spangle as soon as the spangle is contacted by the growth front on
the structure front surfaces which then continues to overgrow the
spaces between the spangles. As soon as the metallic growth front
reaches the next spangle, the whole spangle becomes part of the
cathode deposition area and the lateral growth continues from the
edges of the spangle. In this manner, lateral growth on the
surfaces is accelerated with respect to vertical growth.
Consequently, it is possible to control the lateral overgrowth
speed over non-conductive surfaces as desired. Assuming, for
example, a uniform arrangement of the conductive spangles
(distance: b) and an identical spangle size (characteristic size,
that is, diameter:a) the speed of lateral growth is:
This applies if, with an uncoated surface that is a front surface
without spangle arrangement according to the invention, there is
some growth speed in any direction which can be assumed to be
reasonably true. Otherwise, the equation applies:
Furthermore, by a predetermined non-uniform arrangement of the
spangles or the predetermined arrangement of larger spangles, the
lateral overgrowth speed can be adjusted to requirements of a given
design arrangement, the method according to the invention can
consequently be adjusted to the given requirements, that is, it can
be utilized in a feasible manner.
Spangle geometry, spangle size, spangle distance and spangle
thickness (and consequently, the thickness of the conductive
material) can be selected as desired; they are limited only by the
requirements of the method used for providing the spangles. The
thickness of the spangles may be 10 to 10,000 nm, preferably about
50-300 nm, (like in U.S. Pat. No. 5,073,237 discussed earlier).
Typical dimensions for the spangle diameter are 5 to 50 By
selecting a suitable spangle geometry, such as a frame or ring
shape, the spangle-covered surface area may be limited to a
minimum. It is, for example, without effect on the speed of the
lateral galvanic growth whether the spangles are electrically fully
conductive or whether only their outer edges are electrically
conductive while the center portions of the spangles are
non-conductive.
For the formation of a continuous layer of the electrically
conductive material or surface areas provided with a spangle
pattern, there are at least two possibilities: the molding
procedure wherein, in accordance with the earlier discussed U.S.
Pat. No. 5,073,237, a microstructured plate-like molding tool is
formed, or optical, that is, X-ray depth lithography is utilized.
In the first case, it is necessary to use a plastic material with
thermoplastic properties. In the second case, the plastic consists
of one of the known optical or X-ray resist materials such as
polymethylmethacrylate (PMMA) or a PIQ lacquer.
In both cases the micro structuring has to be done in such a way
that the structure base has a continuous electrically conductive
surface, which in the galvanizing bath, is connected so as to form
a cathode. With a shaping procedure, the structure base can be made
electrically conductive by stamping the structure on a composite
layer of a thermoplastic material with an electrically conductive
top layer (for example a metal or carbon layer). This procedure,
however, has limits with regard to shape: the structure base has to
be a contiguous surface throughout. With X-ray lithography, a
metallic base plate with X-ray resist polymers thereon can be
utilized. This procedure has no limits with regard to the shape
since the metallic base plate always provides for a contiguous
structure base.
For making the pattern of small spangles which are electrically
insulated from one another, there are at least three processes, A,
B, and C which will be described in greater detail on the basis of
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 to FIG. 7 show the process A,
FIG. 8 to FIG. 13 show the process B, and
FIG. 14 to FIG. 18 show the process C.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The various methods will be illustrated for a microstructuring
procedure on the basis of X-ray lithography wherein the plastic
layer (here the layer of X-ray resist material) is covered, before
the micro structuring procedure, with a layer of the electrically
conductive material to form a plate with a conductive surface. Then
the plate is microstructured by X-ray depth lithography. The
advantage of this procedure is that it makes sure that only the
front surfaces of the microstructures are coated but not the
vertical side surfaces of the microstructure bodies. In the
subsequent galvanizing process, first the cavities between the
microstructure bodies are filled starting with the electrically
conductive structure base. As soon as the galvanically deposited
material reaches the front faces of the microstructures, the
spangles of conductive material on the faces are contacted one
after the other by the lateral growth of the metal being deposited,
whereby lateral overgrowth on the front faces is greatly
accelerated. However, since no sudden contact is provided for the
whole front surface, the disadvantages described earlier are
avoided.
FIGS. 1 to 7 show the formation of a standard layer by
microstructure molding and mechanical machining in accordance with
process A.
As shown in FIG. 1, a flat X-ray resist layer 2 of PMMA is
polymerized onto a metallic base plate 1, which is flat on both
sides.
The whole upper side of the X-ray resist layer 2 is then coated
with a layer 3 of an electrically conductive material as shown in
FIG. 2. As electrically conductive material gold, carbon or thin
plastic layers which have been modified so as to be conductive may
be utilized. Suitable processes for applying such a layer are, for
example, sputtering or vapor deposition.
By a vacuum stamping process a metal stamp 4 (form insert) is
impressed into the electrically conductive layer 3 as shown in
FIGS. 3 and 4. Instead of a vacuum stamping process, other molding
procedures such as a reaction casting process may be used. The
metal stamp 4 itself is microstructured in accordance with the
design requirements for the microstructures to be formed. In most
cases, a metal stamp 4 is used for forming the microstructures on
the electrically conductive layer 3 which forms a contiguous
surface in the structure bases from which isolated microstructures
6 projects. The height of the microstructures 6 is basically
unimportant; however with a view to fast and easy mechanical
finishing, it should not be too great (about 2 to 5 .mu.m). A small
microstructure height is also preferable because the metal stamp
can be easily made by optical lithography. Particularly suitable
are metal stamps with pyramid-shaped microstructures thereon, as
they can be obtained by mechanical micromanufacturing methods. With
such structures, it is also possible to vary the width of the
electrically insulating gaps between the conductive spangles by
choosing the cutting depth.
By the microstructuring using the vacuum stamping process, a
projection network is formed on the surface of the X-ray resist
material. This network including the top layer is cut down by
mechanical means (see FIG. 5 such that only isolated spangles of
predefined size remain between the network lines while spangles are
electrically insulated from one another but carry an electrically
conductive surface layer as shown in FIGS. 6 and 7.
FIGS. 8-13 shows a subtractive microstructuring procedure as
represented by process B. Again a metallic base plate 1 is utilized
onto which an X-ray resist layer 2 of PMMA is polymerized as shown
in FIG. 8. Then a thin electrically conductive layer 3 is applied
to the layer 2 as shown in FIG. 9. A light sensitive photo lacquer
8 is then applied to the surface of the electrically conductive
layer 3. The thickness of the photo lacquer coating 8 depends on
the required structuring accuracy and is usually very thin (0.5
.mu.m) as shown in FIG. 10.
A structure pattern is then generated on the photolayer coating 8
by a lithographic procedure wherein a suitable mask 9 such as a
chromium mask, is placed onto the photolacquer coating 8 as shown
in FIG. 11.
After a grid pattern has been removed from the photo lacquer
coating 8 by exposure to light, the exposed portions of the
conductive layer 3 are removed by etching. For this procedure,
isotropic or anisotropic chemical or physical removal processes are
applicable such as liquid chemical etching, plasma etching or
reactive ion etching as indicated in FIG. 12.
After structuring of the conductive layer 3, the photo lacquer 8 is
removed. The then exposed electrically conductive areas form
isolated spangles 7 which have electrically conductive surfaces but
are insulated from each other as shown in FIG. 13.
FIGS. 14-18 show an additive microstructuring procedure as
represented by process C. A metallic base plate 1 onto which an
X-ray resist layer 2 is polymerized as shown in FIG. 14 is coated
with a light-sensitive photo lacquer 8 as shown in FIG. 15 and the
light sensitive coating is then, like in the previous example,
lithographically structured by means of a mask 9 and light exposure
as indicated in FIG. 16.
Then an electrically conductive layer 3 is applied to the whole
surface including the photolacquer areas as shown in FIG. 17.
Then the photolacquer areas are removed. In this step also, the
front faces 10 of the photolacquer areas carrying the electrically
conductive layers 3 are removed. As shown in FIG. 18, the remaining
electrically conductive areas form isolated spangles 7 which are
electrically insulated from one another like those obtained by
processes A and B.
The advantages of the process according to the invention can be
summarized as follows: By providing on the front faces of the micro
structured bodies a pattern of electrically conductive spangles
which, however, are electrically insulated from each other before
the galvanic deposition of metal on the microstructured bodies, it
is possible to adjust the speed of the lateral growth on the front
faces of the micro structured bodies during the galvanic metal
deposition to a large extent depending on design requirements for
the manufacture of form inserts. According to the LIGA (X-ray
lithography and galvanic forming) process this means:
No missing microstructure elements occur in the galvanically formed
metal layer which could otherwise occur when a fully conductive
resist front face is reached by the build-up of metal relatively
early and becomes suddenly fully conductive. As with the
arrangement according to the invention, this surface becomes
conductive only in steps. Faults which occur without the procedure
according to the invention, particularly in the galvanic forming of
stepped microstructures, are eliminated;
Changes in the deposition conditions (such as current density)
which occur during overgrowth of non-conductive front surfaces and
which are difficult to control, become manageable. The surface
increases during lateral growth and, accordingly, the changes in
current density during the metal deposition procedure can be better
predicted. Excessive height differences in the galvanic deposition
layer are avoided. The mechanical properties such as internal
tensions in the deposited layer can be controlled better and are
more uniform.
Below the invention will be described in greater detail on the
basis of exemplary embodiments.
An X-ray resist layer of PMMA was applied to a metallic base plate
and a gold layer of 50 nm thickness was then sputtered onto the
X-ray resist layer. At a temperature of 160.degree. C., a metal
stamp was then pressed onto this layer in a vacuum stamping process
for a stamping period of 5 minutes and with a stamping force of 10
kN. The stamp was then removed at a temperature of about 90.degree.
C. By this process a protruding comb structure was formed in the
resist layer with comb openings of about 20 .mu.m and a web width
of about 4 .mu.m. The overall height of the comb/web structures was
about 4.3 .mu.m.
By grinding down the projecting comb webs (by wet grinding with a
grinder having grain size 1200), the combwebs were cut down to the
structure base whereby an essentially planar resist surface was
obtained having now, however, comb-shaped gold deposits with 20
.mu.m openings separated from each other by insulating resist
surface areas 4 .mu.m wide.
In order to plane remainders of the web structure possibly still
present, the resist surface was pressed against the plane plate in
an additional vacuum stamping step under the same conditions as
described above (method according to process A).
The speed of the lateral growth during galvanic deposition was
measured with resist surfaces pretreated in this manner without
first forming microstructures. In this test, extremely wide
microstructure body front surfaces were insulated.
The speed of lateral growth was checked by coveting the sample in a
nickel sulfamate bath as it is normally used for galvanizing with
nickel at a current density of 1 A/din.sup.2. Subsequently, the
surface profile of the deposited nickel layer was measured at
various places. From the relation of lateral growth to vertical
growth over the contact surfaces, the ratio of the two growth
speeds was determined.
In accordance with the above equation, with the geometry present,
the lateral growth was calculated to be greater than the vertical
growth by a factor of 5.3. By the measurement procedure described
above on the other hand, an average factor of 4.9 with a standard
deviation of 0.24 was calculated.
The height profile of the galvanic deposition showed an essentially
linear decline in the direction of lateral growth. This result was
reproduced in several additional tests.
In another example, a resist layer (PMMA, about 200 .mu.m thick)
was polymerized onto to a base plate (Cu) and treated like in the
previous example to form spangles on its surface. The so prepared
sample was then subjected to X-ray lithography wherein it was
covered with an X-ray mask and exposed to synchrotron radiation.
The irradiated areas were dissolved in a developing bath such that
as product a metallic base plate was obtained onto which plastic
microstructures were disposed which had front surfaces with
electrically conductive spangles disposed thereon such that they
were insulated from each other. In a subsequent galvanic deposition
procedure, metal was deposited on this base plate in a bath (nickel
sulfamate at a current density of 1 A/dm.sup.2 ) until the
microstructures were completely covered with metal. It was found
that the front surfaces were covered with metal substantially
faster than spangle-free surfaces and that the height differences
of the galvanic depositions were substantially smaller than in
previous tests in which no electrically conductive spangles were
disposed on the front surfaces. The front faces of the
microstructure were more than 1 mm wide at certain points.
* * * * *